Session Initiation Protocol (SIP)
IP Multimedia Subsystem (IMS)
Environment
Access network
Web services
The services of Cloud computing can be divided into three categories:
1. Software-as-a-Service (SaaS), in which a vendor supplies the hardware infrastructure, the software product and interacts with the user using a portal (software on demand, pay-as-you-go).
2. Platform-as-a-Service (PaaS), in which a set of software and development tools are hosted by a provider on the provider's infrastructure, for example, Google's AppEngine.
3. Infrastructure-as-a-Service (IaaS), which involves virtual server instances with unique IP addresses and blocks of on-demand storage, for example, Amazon's Web services infrastructure.
Cloud Computing
Cloud Computing
Virtualization Web Application Frameworks
Information demand and supply (Open APIs)
Ubiquitous Network Access
Offloading
The offloading of a mobile computing task is a trade-off between the energy used for local processing and the energy required for offloading the task, uploading its data, and downloading the result, if necessary.
One can express the offloading energy trade-off as follows: Etrade = Elocal − Edelegate > 0, where Elocal is the
energy used for complete local execution, and Edelegate is the energy used if the task is offloaded from the perspective of the mobile device.
If Etrade is greater than zero, then there is an energy benefit for delegating the task to the cloud.
What can be offloaded?
Completion notification and mobile push
Application execution Google docs, Windows Office
Connection management BitTorrent! Large downloads
Example of Offloading: Indexing
To offload indexing Transmit entire file to the cloud service Wait for response Receive file summary
High energy savings can be obtained when offloading CPU-intensive tasks
With N900 and WLAN 700kB/s: 96.5% savings! With WLAN 100kB/s this is reduced to 83.7%
Virtualization
Virtualization system is a framework that combines or divides computing resources to present a transparent view of one or more environments Hardware/software partitioning (or
aggregation) Partial or complete machine simulation Emulation (can be partial or complete) Time-sharing
Mobile virtualization
Server Based Virtualization of Desktop Infrastructure
Moving the desktop to a virtualized image in the data center allows the complex components to be protected and componentized Workload isolation and migration Application virtualization
Virtualization is a possible solution to the fragmentation problem
http://www.vmware.com/technology/mobile/
Virtualization for offloading Running applications in a base station, nearby server, in the
cloud Research proposals
An Application-layer control (signaling) protocol for creating, modifying and terminating sessions with one or more participants.
Sessions include Internet multimedia conferences, Internet telephone calls and multimedia distribution.
Members in a session can communicate via multicast or via a mesh of unicast relations, or a combination of these.
Text based, model similar to HTTP.
Current system: Signalling System 7 (SS7).
SIP History
Mid-1990s, emerged from the research of Dr. Henning Schulzrinne, Columbia University, on Multi-party Multimedia Session Control (MMUSIC)
1996, submitted to the Internet Engineering Task Force (IETF) and developed by the SIP Working Group
1999, first published as IETF RFC 2543 2000, selected by 3GPP 2002, RFC 3261 (with further
supplements in other RFCs)
SIP features
User location: determination of the end system to be used for communication
User capabilities: determination of the media and media parameters to be used
User availability: determination of the willingness of the called party to engage in communications
Call setup: "ringing", establishment of call parameters at both called and calling party
Call handling: including transfer and termination of calls
SIP messages
Start Line (Request Line or Status Line) message type (method type & URI in
requests, and response code in responses) protocol version
Headers fields to convey message attributes can span multiple lines, appear multiple
times, take multiple comma-separated values Body (Content)
to describe the session to be initiated to contain opaque textual or binary data
SIP
1. SIP Addressing 2. Locating a SIP Server 3. Sending SIP Requests: SIP
Transactions 4. SIP Methods 5. SIP Responses 6. Subsequent Requests and Responses
Proxy Server Proxy Server
5. INVITE To:sip:bob@test.com
14. 200 OK
16. 180 ACK
The IP Multimedia Subsystem Provides Multimedia Services Across Networks (fixed & mobile), such as: Instant Messaging, Video Sharing, Push-To-Talk,
Gaming, Video Conferencing
IMS Uses SIP protocol To Setup Multimedia Sessions Over IP Network
SIP is a signalling protocol to: Locate user given SIP Universal Resource
Identifier (URL) (e.g., sip:jane@isp.com) Set up session and negotiate its parameters
IMS Proxies I
CSCF = Call State Control Function
A Proxy-CSCF (P-CSCF) is a SIP proxy that is the first point of contact for the IMS terminal it is assigned to an IMS terminal during registration, and
does not change for the duration of the registration it sits on the path of all signalling messages, and can
inspect every message it authenticates the user and establishes an IPsec
security association with the IMS terminal. it can also compress and decompress SIP messages
using SigComp, which reduces the round-trip over slow radio links
it may include a Policy Decision Function (PDF), which authorizes media plane resources e.g. quality of service (QoS) over the media plane. It's used for policy control, bandwidth management, etc. The PDF can also be a separate function.
it also generates charging records
IMS Proxies II
A Serving-CSCF (S-CSCF) is the central node of the signalling plane it is always located in the home network. It uses Diameter
Cx and Dx interfaces to the HSS to download and upload user profiles — it has no local storage of the user data. All necessary information is loaded from the HSS
it handles SIP registrations, which allows it to bind the user location (e.g. the IP address of the terminal) and the SIP address
it sits on the path of all signaling messages, and can inspect every message
it decides to which application server(s) the SIP message will be forwarded, in order to provide their services
it enforces the policy of the network operator
An Interrogating-CSCF (I-CSCF) is another SIP function located at the edge of an administrative domain
IMS
User A
Location Query
User B
Session-Based Non-Session-Based
Provider of the WS Service Requestor
Any consumer / client Service Registry
logically centralized directory of services
A protocol stack is needed to support these roles
Web Services Protocol Stack Message Transport
Responsible for transporting messages HTTP, BEEP
XML Messaging Responsible for encoding messages in
common XML format XML-RPC, SOAP
Service Description Responsible for describing an interface to a
specific web service WSDL
What is SOAP?
Exchange of structured and typed information Between peers in decentralized fashion Using different mediums: HTTP, Email, ..
Request-reply and one-way communication are supported Note that XML infoset is an abstract specification
On-the-wire representation does not have to be XML 1.0! SOAP 1.2 ”HTTP Subset”. SOAP as HTTP extension Specifications
SOAP Version 1.2 Part 0: Primer SOAP Version 1.2 Part 1: Messaging Framework SOAP Version 1.2 Part 2: Adjuncts SOAP Version 1.2 Specification Assertions and Test Collection
REST
REST (Representational State Transfer) (Roy Fielding, PhD thesis) Architectural style of networked systems Applications transfer state with each resource representation
Representations of the data are transmitted State is a property of a resource
Resources Any addressable entity Web site, HTML page, XML document, ..
URLs Identify Resources Every resource uniquely identifiable by a URI
REST II
Uses standards Addressing and naming: URI Generic resource interface: HTTP GET,
POST, PUT, DELETE Resource representations: HTML, XML,
GIF,.. Media types: MIME
application state Just resources and URIs
Event-based Systems and Publish/ subscribe
Event delivery from publishers to subscribers Event is a message with content One-to-many, many-to-many Builds on messaging systems and store-and-forward
A frequently used communication paradigm Decoupling in space and time Solutions from local operation to wide-area networking Proposed for mobile/pervasive computing
The event service is a logically centralized service Basic primitives: subscribe, unsubscribe, publish
Various routing topologies and semantics
Event Systems I
Traditional MoM systems are message queue based (one-to-one)
Event systems and publish/subscribe are one-to-many or many-to-many One object monitors another object Reacts to changes in the object Multiple objects can be notified about changes
Events address problems with synchronous operation and polling
In distributed environments a logically centralized service mediates events anonymous communication expressive semantics using filtering
Notification Consumer
Notification Engine
Subscription Manager
appropriate consumers
Subscriptions
Push versus Pull May be implemented using RPC, unicast, multicast,
broadcast,.. Three main patterns
Notifier architectural pattern Used by many research systems
Event channel Used in CORBA Event/Notification Service
Filtering improves scalability / accuracy Research topic: content-based routing
Tuple Spaces
Tuple-based model of coordination The shared tuple space is global and persistent Communication is
decoupled in space and time implicit and content-based
Primitives In, atomically read and removes a tuple Rd, non-destructive read Out, produce a tuple Eval, creates a process to evaluate tuples
Examples: Linda, Lime, JavaSpaces, TSpaces
Java Message Service (JMS)
One-to-one
Topic-based publish/subscribe SQL for filtering messages at the topic event queue One-to-many
Message types: Map, Object, Stream, Text, and Bytes
Durable subscribers Event stored at server if not deliverable
Transactions with rollback
Acknowledges Sends
The Data Distribution Service for Real-Time Systems (DDS)
The specification defines an API for data- centric publish/subscribe communication for distributed real-time systems.
DDS is a middleware service that provides a global data space that is accessible to all interested applications.
DDS uses the combination of a Topic object and a key to uniquely identify instances of data-objects.
Content filtering and QoS negotiation are supported
DDS is suitable for signal, data, and event propagation.
DDS
Publisher
DataWriter
Subscriber
DataReader
Subscriber
DataReader
Data-Object Identified by means of the Topic Identified by means
of the Topic
WHEN to sync? manually Automatically
Synchronization and replication store data in a number of locations fault tolerance, but... most copies unavailable most of the time
Synchronization models
HOW to sync? permit only one modifiable copy of data
lock on data hub-and-spoke model
multiple copies can be independently modified more flexible more complex to implement the sync process
Synchronization models Sync process
modified
data replica
to build a synchronized version
Synchronization models Sync process
process clean / dirty status
(e.g. in file system) • comparison of all the timestamps
– time / resource consuming! • monitoring file system for changes • use dir timestamp if equal to last
modified contained file
semantics of modification time when a file timestamp is actually
modified? • content modifying, file renaming,
file relocation?
build a synchronized version
opaque data (e.g. binary, pictures) • ask the user which version to use
structured data (e.g. XML) • edit logs • state comparison • both (can) use the latest common
ancestor as comparison aid
Synchronization models Sync process
reconciliation
type of modifications (inside a single file): insertion deletion moving changing
moving often as deletion + insertion use of unique ID per piece of
structured content
Remote Differential Compression (RDC) Microsoft Windows Server 2003 R2 / 2008 allows data to be synchronized between
two or more computers, using compression techniques to minimize the amount of data sent across the network.
Synchronization models data sync algorithms & tools
Remote Differential Compression (RDC) files (to be synced) divided into chunks of data
chunk bounded using an incremental fingerprint function
MD4 hash calculated for each chunk comparison of MD4 lists (signature, one per file) transfer only of missing / different chunks can be applied recursively!
original file size 9GB signature 81MB signature of signature 6MB
Synchronization models data sync algorithms & tools
publish / subscribe
for update propagation - data channel each edit gets immediately published as a event continuous reconciliation multiple users
for update detection an update is advertised to all subscribers
Sync in middleware
Synchronization Markup Language
Interoperable protocol to sync data
Case studies: SyncML
update propagation transfer of updates among devices
client-server architecture
based on “edit log” model addition, delete, replace of objects unique ID
data type & data store independent
Notification of conflicts
Case studies: SyncML
Pervasive computing middleware Projects Key Issues
UIC Heterogeneity of devices and networks: It helps users to specialize to the particular properties of different devices and network environments
X-Middle Disconnected operations in mobile applications: It allows mobile users to share data when they are connected, or replicate the data and perform operations on them off-line when they are disconnected; data reconciliation takes place when user gets reconnected
Gaia Dynamic adaptation to the context of mobile applications: It supports the development and execution of portable applications in active spaces
Lime Programming constructs which are sensitive to the mobility constraints: It explores the idea by providing programmers with a global virtual data structure and a tuple space (Tspace), whose content is determined by the connectivity among mobile hosts
Tspaces Asynchronous messaging-based communication facilities without any explicit support for context-awareness: It explores the idea of combination of tuple space (Tspace) and a database that is implemented in Java. Tspace targets nomadic environment where server contains tuple databases, reachable by mobile devices roaming around
L2imbo QoS monitoring and control by adapting applications in mobile computing environment: It provides the facilities of multiple spaces, tuple hierarchy, and QoS attributes